1. Field of the Invention
The present invention relates to a center electrode assembly and a nonreciprocal circuit device which may constitute an isolator or a circulator for use in, for example, a microwave band, and relates to a communication apparatus including this nonreciprocal device.
2. Description of the Related Art
A center electrode assembly shown in FIGS. 30A and 30B is known for use in a concentrated-constant type isolator (nonreciprocal circuit device) adopted in mobile communication equipment such as mobile telephones. This center electrode assembly 200 is formed by wrapping a disk shaped microwave ferrite 201 in an electrode assembly 210 including three center electrodes 211, 212, and 213.
The electrode assembly 210 is formed by extending outward the center electrodes 211, 212, and 213 at predetermined angles from the center planar portion (ground electrode) 215. The center electrodes 211 and 212 are formed of one line, while the center electrode 213 is formed of two lines. In assembly, firstly the center planar portion 215 is abutted against the bottom surface of the ferrite 201, then the center electrodes 211, 212, and 213 are wrapped around the top surface of the ferrite 201 across the side surface thereof (by making folded portions marked xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d), and these center electrodes are crossed with one another at predetermined crossing angles, on the top surface of the ferrite 201.
A nonreciprocal circuit device having this type of center electrode assembly 200 is mainly used in mobile communication equipment, and significant progress is being made in miniaturizing it. Since the electrode assembly 210 requires more miniaturization, the line width of each of the center electrodes 211, 212, and 213 is being made smaller. Such center electrodes are formed by press work using a mold or by etching work, but there are limits to the working accuracy available. It is, therefore, difficult to form all center electrodes so as to have two lines, and currently, at least one of them is generally formed of one line.
FIG. 31 shows another conventional center electrode assembly. In this center electrode assembly 240, an input center electrode 271, an output center electrode 272, and a terminal center electrode 273 are arranged on the top surface of a microwave ferrite 270 with insulating sheets 220 interposed between them so that the crossing angle G formed among mutually crossing center lines thereof becomes about 120xc2x0. First ends of the center electrodes 271, 272, and 273 are electrically connected to port portions P1, P2, and P3, respectively. The other ends of the center electrodes 271, 272, and 273 extend across the side surface of the ferrite 270, and are electrically connected to ground electrode 276 provided on the bottom surface of the ferrite 270. The ground electrode 276 covers substantially the entire bottom surface of the ferrite 270.
In a center electrode assembly incorporated into a concentrated-constant type nonreciprocal circuit device, if the crossing angle formed among three center electrodes varies, it will significantly influence the electrical characteristics thereof such as the insertion loss and the isolation. It is, therefore, very important to ensure the stabilization of the crossing angle.
However, in the conventional center electrode assembly 200 shown in FIGS. 30A and 30B, since each of the center electrodes has a small line width, there is the risk that a line may break due to vibration and heating during assembly or during operation of communication equipment in which the center electrode assembly is incorporated. Such line breakage occurs especially at folded portions xe2x80x9caxe2x80x9d and/or xe2x80x9cbxe2x80x9d. In particular, the line breakage of a center electrode formed of one line could cause a critical defect.
As indices of the performance of an isolator, there are insertion loss and isolation. The lower the insertion loss, the better the isolator. The wider the isolation bandwidth, the better the isolation characteristic. In FIG. 32, there is shown the relationship between the insertion loss 280 and the isolation characteristic 282 of the isolator in which the above-described center electrode assembly 240, of which the crossing angle G is 120xc2x0, is incorporated (see the dotted lines).
Now, as a method for improving the insertion loss, it is known to increase the crossing angle G formed between the input center electrode 271 and the output center electrode 272. For example, in FIG. 32, there is shown the relationship between the insertion loss 281 and the isolation characteristic 283 of the isolator incorporating the above-described center electrode assembly 240 when the crossing angle G is changed to 125xc2x0 (see the solid lines). However, although this method can improve the insertion loss, this method reduces the isolation bandwidth, and is prone to increase the fraction of defective manufactured parts due to variations in characteristics among production lots of the center electrode assembly 240.
Furthermore, enlarging the crossing angle formed between the input center electrode 271 and the output center electrode 272 reduces the distance A-Axe2x80x2 from the intersection point A (see FIG. 31) of the edge of the input center electrode 271 and that of the output center electrode 272 to the edges of the insulating sheets 220. As a result, if the insulating sheets 220 are displaced to the position 220a indicated by the two-dot chain line 220a, short-circuit failures are prone to occur between the input center electrode 271 and the output center electrode 272.
The present invention provides a center electrode assembly and a nonreciprocal circuit device, and a communication apparatus incorporating them, which have stable physical properties and high reliability, and which eliminate the risk of line breakage of the center electrodes thereof.
The present invention also provides a center electrode assembly and a nonreciprocal circuit device, and a communication apparatus incorporating them, which have improved the insertion loss without impairing other electrical characteristics, and which are less likely to have short-circuit failures.
In order to provide the foregoing, the present invention, in a first aspect, provides a center electrode assembly comprising an electrode assembly wherein a plurality of center electrodes extends outward from the center planar portion thereof at a predetermined angular distance; and a ferrite. In this center electrode assembly, the center planar portion is abutted against the bottom surface of the ferrite, then the center electrodes are wrapped around the top surface of the ferrite across the side surface thereof, and the center electrodes are crossed with each other on the top surface of the ferrite. At least one center electrode is formed of one line, and the line width of the above-mentioned center electrode is enlarged where it crosses the side surface of the ferrite near the center planar portion.
The present invention, in a second aspect, provides a center electrode assembly comprising an electrode assembly wherein a plurality of center electrodes extends outward from the center planar portion thereof at a predetermined angular distance; and a ferrite. In this center electrode assembly, the center planar portion is abutted against the bottom surface of the ferrite, then the center electrodes are wrapped around the top surface of the ferrite across the side surface thereof, and the center electrodes are crossed with each other on the top surface of the ferrite. At least one center electrode is formed of one line, and the line width of the above-mentioned center electrode is larger near the ferrite edge than near the ferrite center.
In the center electrode assembly in accordance with the first and second aspects, the ferrite is wrapped in the center electrodes by folding the center electrodes at the ferrite edge portions thereof near the center planar portion, that is, at the cold ends of the center electrodes. Since the ferrite edge portions thereof at the cold ends, which are folded portions, are formed wide, the ferrite edge portions have greater strength, thereby significantly reducing the risk of line breakage. Moreover, the crossing angle formed between the central electrodes is stabilized, resulting in superior electrical characteristics.
In the center electrode assembly in accordance with the first and second aspects, when there are provided first, second, and third center electrodes, it is preferable, for preventing electrical short circuits between the first and second center electrodes, that the crossing angle xcex812 formed by a first center electrode and a second center electrode which is adjacent to the first center electrode on one side, be greater than the crossing angle xcex831 formed by the first center electrode and a third center electrode which is adjacent to the first center electrode on the other side; that is, xcex812 greater than xcex831.
It is also preferable that the width of the ferrite edge portion of the first center electrode at the cold end be larger at the portion thereof close to the second center electrode than at the portion thereof close to the third center electrode, with respect to the center line at the ferrite center portion. The same effect can be obtained, even when the relationship between the crossing angles xcex812 and xcex831 is xcex812 less than xcex831, by making the width of the ferrite edge portion of the first center electrode at the cold end larger at the portion thereof close to the third center electrode than at the portion thereof close to the second center electrode, with respect to the center line at the ferrite center portion.
Also, it is preferable that the width of the center electrode formed of one line gradually increase toward the ferrite edge portion for eliminating a rapid change in the line width and for relaxing the stress concentration.
In accordance with a third aspect, the present invention provides a center electrode assembly comprising an electrode assembly wherein a plurality of center electrode extends outward from the center planar portion thereof at a predetermined angular distance; and a ferrite. In this center electrode assembly, the center planar portion is abutted against the bottom surface of the ferrite, then the center electrodes are wrapped around the top surface of the ferrite across the side surface thereof, and the center electrodes are crossed with each other on the top surface of the ferrite. Also, each of the center electrodes has a smooth arc portion, and is continuous, with respect to the center planar portion.
The center electrode portions which are continuous with the center planar portion, correspond to the folded portions. Since each of these portions has a smooth arc shape, the stress concentration is relaxed, the risk of line breakage is significantly reduced, and the crossing angle formed between the center electrodes is stabilized, resulting in superior electrical characteristics.
In accordance with a fourth aspect, the present invention provides a center electrode assembly comprising a ferrite; an input center electrode, an output center electrode, and a terminal center electrode which are provided on a first main surface of the ferrite so as to intersect one another at a predetermined angle; a ground electrode which is disposed on a second main surface of the ferrite, and to which one end portion of each of the input center electrode, the output center electrode, and the terminal center electrode is connected; and an input port portion, an output port portion, and a terminal port portion which are connected to the other ends of the input center electrode, the output center electrode, and the terminal center electrode, respectively. In this center electrode assembly, at least one of the input center electrode, output center electrode, and terminal center electrode has a shape with a gradually-increasing width wherein the electrode width on the ground electrode side is larger than that on the port portion side.
With these features, since at least one of the input center electrode, output center electrode, and terminal center electrode has a gradually-increasing width wherein the electrode width on the ground electrode side is larger than that on the port portion side, although the ground electrode side exhibits the largest high-frequency currents, the concentration of high-frequency currents there is relaxed, and the insertion loss is improved without impairing the electrical characteristics such as the isolation characteristic.
The arrangement may be such that each of the input center electrode and the output center electrode has a gradually-increasing width on one side thereof, wherein the electrode width on the ground electrode side is larger than that on the port portion side, by extending the edge thereof closest to the terminal port portion, in the electrode width direction. These features prevent short-circuit failures among the center electrodes from occurring.
The nonreciprocal circuit device and a communication apparatus in accordance with the present invention have the center electrode assembly with the above-described features, thereby providing stable electrical characteristics and improving the reliability thereof.
The above and other features and advantages of the present invention will be clear from the following detailed description of embodiments of a center electrode assembly, a nonreciprocal circuit device, and a communication apparatus in accordance with the present invention in conjunction with the accompanying drawings. In the drawings illustrating these embodiments, like members and parts are given the same reference numerals, and repeated descriptions are omitted.